When setting DND or Away on a D70, it does not update the astDB and therefore does not reflect presence in fop2. Would I need to create a custom app in order to get the behavior of also setting presence in astDB?

If you're using DPMA, then the presence is maintained in AstDB. If you're not using DPMA, then you don't get the full status app, and you only get available and DND, where DND returns a 486 when the phone is called.